1. Field of the Invention
The present invention relates to a semiconductor substrate having a layer of gettering sink material formed thereon, a method of manufacturing the semiconductor substrate and a semiconductor device using the semiconductor substrate.
2. Description of the Background Art
A semiconductor device is fabricated by combination of the steps of film formation, washing, thermal treatment, photolithography and the like. Heavy metals such as Fe, Ni, Cr, Cu, Zn and the like are inevitably mixed in, for example, a washing solution for use in the step of washing and resist for use in the step of photolithography. Therefore, these heavy metals often enter a semiconductor device.
One example of the problems that occur when heavy metals enter a semiconductor device is that, when heavy metals enter a PN junction, the region of the junction acquires a crystal defect to cause current leakage.
Among steps for manufacturing a semiconductor device, the step of removing heavy metals which entered the semiconductor device is referred to as gettering. There are various kinds of gettering. The following description will be given to gettering carried out by formation of a poly-crystalline silicon film on the rear surface, having no elements formed thereon, of the surface of a silicon single-crystalline wafer.
When the poly-crystalline silicon film is formed on the rear surface of the silicon single-crystalline wafer, gettering is carried out on the following two theories.